1. Field of the Invention
The present invention relates generally to a microprocessor based equipment, such as a battery operated portable personal computer. More specifically, the invention relates to a drive control system for optimally controlling a driving condition of a microprocessor depending upon operational state thereof.
2. Description of the Related Art
As disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2-178818, for example, power saving control is well-known in the art to interrupt power supply to those section of a computer system which are not executing any substantial task for reducing total power consumption of the computer system. Such technology has already been applied to field products. In the field of battery-operated personal computers including a lap-top computer, much study has been given in the power saving technology of this type in the sake of maximizing the system uptime with a smaller and lighter battery.
Conventionally, two types of functions for placing the personal computer into a stand-by state, i.e. so-called a rest mode function and a sleep mode function are provided in certain types of personal computer systems. The rest mode function is performed for automatically switching an operational clock frequency of the computer system from 16 Mhz in the normal operational mode to 1 Mhz when a CPU is held inoperative state for a predetermined period of time. If a further predetermined period is elapsed while the computer system is held in the rest mode state, the sleep mode is automatically initiated to shut down the power supply. In either mode of operation of the computer system, the normal mode operation can be resumed by operating an arbitrary key. In many cases, the predetermined period of time for initiating the stand-by mode can be arbitrary set by the user through manual setting operation.
As can be appreciated, conventionally, the computer system is situated into the power saving state (i.e. the above-mentioned stand-by mode) in terms that "the CPU is held substantially inoperative state for a predetermined period of time". In practice, the operational state of the computer system is changed over from the normal state into the power saving state in absence of any external factor for initiating substantial task of the CPU, such as input through entry from a keyboard or from a communication supervisory system or so forth, for the predetermined period of time.
In general, while the personal computer is executing an application software, such as a Japanese wordprocessor, a table calculation or so forth, the process speed of the modern and high performance microprocessor (CPU) is much higher than entry speed of the operation through a keyboard. Therefore, in the CPU operation, the CPU frequently falls into a substantial waiting state, in which a trigger factor for performing next task is waited. Even though each individual period where the CPU is situated in the substantial waiting state is relatively short, accumulation of such period over total operation period of the personal computer becomes substantial. Therefore, if the CPU is switched into the power saving state, in which the power consumption and the processing speed of the CPU is relatively low, by detecting the substantial waiting state, substantial effect in saving power consumption can be achieved.
On the other hand, saving of the power consumption in the microprocessor is effective not only for expanding available period of a battery in the battery operated personal computer but also for reducing heat to be generated in the microprocessor based equipment. Namely, greater performance and higher processing speed in the microprocessor requires higher power consumption. Higher consumption naturally results in generation of greater amount of heat to induce a potential overheating problem. Therefore, in designing a notebook type personal computer, an electronic pocketbook or so forth, it is important task to consider the installation design with taking a heat radiation into account in order to avoid overheating of components which generate heat. Naturally, by employing sufficient capacity of radiation fan or radiation fin, the overheating problem in the elements can be successfully avoided. However, on the other hand, the large capacity fan or fin requires substantial space for installation and causes substantial increase of the weight and thus serve for burdening down-sizing of the overall size and reduction of the weight of the equipments, such as the notebook type personal computer, the electronic pocket book or so forth.